The potential benefit of DPAV can already be checked with the static PAV.
To do this, first of all DPAV is activated (DPAV_SET_ON=YES).
The DPAV_CHK_RESET statement then defines the time at which a check should begin. The following can be queried later (for example an hour or a day later):
Query of all devices for which an additional alias device would have made sense (DPAV_CHK_DEV? statement)
Query of the existing alias device and their I/O activity (DPAV_CHK_ALI? statement)
The check period taken into account always begins with the DPAV_CHK_RESET statement and ends at the time a query is made.
As the check takes place in normal DPAV mode, alias names can be activated immediately after a check.
Starting the check
DPAV_CHK_RESET |
DPAV_CHK_RESET |
Querying the devices for which an alias device would make sense
DPAV_CHK_DEV checks the devices for which an alias device would have made sense and displays the devices with the frequency > 0.
DPAV_CHK_DEV? |
DPAV_CHK_DEV?mask |
mask | Complete or masked specification of a mnemonic device name. The following specifications are possible: | |
* | All devices are checked. | |
n* | All devices whose names begin with n are checked. | |
nm* | All devices whose names begin with nm are checked. | |
nml* | All devices whose names begin with nml are checked. | |
nmlo | The device with the name nmlo is checked. | |
Querying existing alias devices and their I/O activity
DPAV_CHK_ALI? lists existing alias devices and displays their I/O activity (average I/Os per second). The I/O activity relates only to the home system. In VM mode, additional I/Os could be active on other guest systems.
DPAV_CHK_ALI? |
DPAV_CHK_ALI?mask |
mask | Complete or masked specification of a mnemonic device name. The following specifications are possible: | |
* | All alias devices are listed. | |
n* | All alias devices whose names begin with n are listed. | |
nm* | All alias devices whose names begin with nm are listed. | |
nml* | All alias devices whose names begin with nml are listed. | |
nmlo | The alias device with the name nmlo is listed. | |
Example
Two I/O requests are always pending for device 3801 which is connected to controller 3800 (devices 3800 ... 38FF); an alias device 3807 is assigned. Multiple I/O requests are often pending for device 3803; however, device 3803 is not assigned an alias device.
Querying all devices for which an additional alias device would make sense
DPAV_CHK_DEV?*
Output:
UNIT NAME | FREQUENCY % -----------+------------ 3803 | 100
The requirements for an additional device were satisfied 100% for device 3803.
Querying existing alias devices and their I/O activity
In the next step a check is made to see whether alias devices exist on controller 3800:
DPAV_CHK_ALI?38*
Output:
UNIT NAME | I/O PER SEC -----------+------------ 380A | 0 380B | 0 380C | 0 380D | 0 380E | 0 380F | 0 3804 | 0 3805 | 0 3806 | 0 3807 | 2569 3808 | 0 3809 | 0
2569 I/Os per second are active on alias device 3807; the remaining alias devices show no I/O activity on the home system.
Activating alias devices for DPAV
The following assignment of alias devices is made on the basis of the check that was performed:
DPAV_DEV_ADD=D-R(3804,3806)
DPAV_DEV_ADD=D-R(3808,380F)
Alias device 3807 remains permanently assigned to device 3801; the other alias devices on controller 3800 are activated for DPAV.
If no alias devices are generated on the controller, these can be configured (using IOGEN or /ADD-IO-UNIT).
Starting another check
The effectiveness of the new assignment of the alias devices is checked by starting a new check period:
DPAV_CHK_RESET
The devices for which an alias device would make sense are then queried again (after a few minutes):
DPAV_CHK_DEV?*
Output:
UNIT NAME | FREQUENCY %
-----------+------------
|
Device 3803 is no longer listed.